Synthesis of a dibenzo-BODIPY-incorporating phenothiazine dye as a panchromatic sensitizer for dye-sensitized solar cells

For the application of metal-free organic sensitizers in dye-sensitized solar cells (DSSCs), a boron dibenzopyrromethene (dibenzo-BODIPY)-conjugated phenothiazine dye with cyanoacrylic acid as an anchoring group 1 was synthesized and characterized. It showed an intense absorption band at 638 nm as the lambda(max) value and a molar extinction coefficient (epsilon) of 1.23x10(5) M-1 cm(-1). In addition, a relatively small but significant peak was observed at 440 nm (epsilon = 1.80x10(4) M-1 cm(-1)). Such panchromatic features allowed the fabrication of a DSSC with an excellent short-circuit current density (J(sc)) of 19.09 mA cm(-2) under 100 mW cm(-2) AM1.5G simulated light. The corresponding external quantum efficiency (EQE) indicated that the cell converted the light to a photocurrent in a wide wavelength region up to 780 nm, resulting in a power conversion efficiency (PCE; eta) of 7.69% in an I-/I-3(-) redox couple electrolyte without the addition of any coadsorbents. When compared to the control cell loaded with a cycanoacrylic acid-appended phenothiazine 2, the PCE value of the 1-loaded cell was 1.5 times larger than that of the control cell because of significant enhancements in both J(sc) and open-circuit voltage (V-oc). Electrochemical impedance analysis (EIS) suggested attenuation of the charge recombination when using 1 as a sensitizer. In this way, the 1-loaded cell showed relatively good DSSC properties comparable to those of the cell with N719 (eta = 7.15%) under the same conditions.